Spring Cloud Dataflow: issue with updating stream

Question

I'm trying to understand how Spring cloud dataflow server distinguish if an update to a stream has changes.

I have such a stream

{
  "name": "test-stream",
  "dslText": "source --username=test | sink",
}

Then I sent an update request and it went through. I can see the new property test added to the source on the dashboard

POST /streams/deployments/update/test-stream

{
  "releaseName": "test-stream",
  "packageIdentifier": {
    "packageName": "test-stream",
    "packageVersion": null
  },
  "updateProperties": {
    "app.source.username": "test"
    "app.source.test": "test"
  },
}

Then I sent another update request to remove the property test.

POST /streams/deployments/update/test-stream

{
  "releaseName": "test-stream",
  "packageIdentifier": {
    "packageName": "test-stream",
    "packageVersion": null
  },
  "updateProperties": {
    "app.source.username": "test"
  },
}

But this returns an error Package to upgrade has no difference than existing deployed/deleted package. Not upgrading.

Any idea?